PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4

Open
Open
PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4

Description

@rakhimovv
rakhimovv
opened on Jul 23, 2026

Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.

I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.

Setup

  • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
  • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
  • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
  • Reflection budget: 3 iterations per prompt.

What I observe

The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.

What I've already ruled out

To eliminate my own mistakes first:

  • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
  • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
  • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).

Questions

  1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
  2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
  3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
  4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
  5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
  6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?

Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.

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      , 'i'); if (__m === '*' || __re.test(location.href)) { injectUserscript("// Add copy buttons to all 
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      Skip to content
      PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
      Open
      Open
      PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
      Description
      @rakhimovv
      rakhimovv
      opened on Jul 23, 2026
      Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
      I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
      Setup
      • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
      • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
      • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
      • Reflection budget: 3 iterations per prompt.
      What I observe
      The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
      What I've already ruled out
      To eliminate my own mistakes first:
      • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
      • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
      • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
      Questions
      1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
      2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
      3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
      4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
      5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
      6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
      Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
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var __m = "*";
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          Skip to content
          PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
          Open
          Open
          PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
          Description
          @rakhimovv
          rakhimovv
          opened on Jul 23, 2026
          Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
          I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
          Setup
          • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
          • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
          • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
          • Reflection budget: 3 iterations per prompt.
          What I observe
          The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
          What I've already ruled out
          To eliminate my own mistakes first:
          • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
          • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
          • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
          Questions
          1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
          2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
          3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
          4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
          5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
          6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
          Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
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, 'i');
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(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

              Skip to content
              PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
              Open
              Open
              PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
              Description
              @rakhimovv
              rakhimovv
              opened on Jul 23, 2026
              Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
              I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
              Setup
              • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
              • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
              • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
              • Reflection budget: 3 iterations per prompt.
              What I observe
              The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
              What I've already ruled out
              To eliminate my own mistakes first:
              • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
              • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
              • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
              Questions
              1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
              2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
              3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
              4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
              5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
              6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
              Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
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, 'i');
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})();
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try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

                  Skip to content
                  PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
                  Open
                  Open
                  PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
                  Description
                  @rakhimovv
                  rakhimovv
                  opened on Jul 23, 2026
                  Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
                  I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
                  Setup
                  • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
                  • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
                  • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
                  • Reflection budget: 3 iterations per prompt.
                  What I observe
                  The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
                  What I've already ruled out
                  To eliminate my own mistakes first:
                  • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
                  • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
                  • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
                  Questions
                  1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
                  2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
                  3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
                  4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
                  5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
                  6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
                  Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
                  Metadata
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, 'i');
if (__m === '*' || __re.test(location.href)) {
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(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

                      Skip to content
                      PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
                      Open
                      Open
                      PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
                      Description
                      @rakhimovv
                      rakhimovv
                      opened on Jul 23, 2026
                      Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
                      I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
                      Setup
                      • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
                      • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
                      • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
                      • Reflection budget: 3 iterations per prompt.
                      What I observe
                      The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
                      What I've already ruled out
                      To eliminate my own mistakes first:
                      • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
                      • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
                      • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
                      Questions
                      1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
                      2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
                      3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
                      4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
                      5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
                      6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
                      Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
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, 'i');
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                          Skip to content
                          PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
                          Open
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                          PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
                          Description
                          @rakhimovv
                          rakhimovv
                          opened on Jul 23, 2026
                          Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
                          I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
                          Setup
                          • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
                          • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
                          • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
                          • Reflection budget: 3 iterations per prompt.
                          What I observe
                          The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
                          What I've already ruled out
                          To eliminate my own mistakes first:
                          • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
                          • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
                          • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
                          Questions
                          1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
                          2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
                          3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
                          4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
                          5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
                          6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
                          Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
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                              PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings? #4
                              Open
                              Open
                              PostProcess / 4D-dynamics loop rarely converges within the reflection budget: expected success rate and critic settings?#4
                              Description
                              @rakhimovv
                              rakhimovv
                              opened on Jul 23, 2026
                              Hi, and thanks for releasing the code. I've enjoyed digging into the code-as-world-model idea.
                              I'm reproducing the pipeline as an independent check, and I keep hitting very low convergence in the PostProcess / 4D-dynamics stage. Getting to an end-to-end run took a fair amount of reconstruction on my side, mostly around the dynamics stage. So before I draw any conclusions, I'd like to rule out that my reconstruction, rather than the method itself, is what's failing. A few implementation specifics would help me line my setup up with yours.
                              Setup
                              • Object, Scene, and PostProcess streams run in order, with the VLM critic in the loop as described in the paper.
                              • Models: Gemini 3 Pro for both the code generation and the VLM critic, matching the all-Gemini configuration in your appendix.
                              • Infinigen v1.19.0; Blender 4.3 for the bake and render step, bpy 4.2 for scene and object generation.
                              • Reflection budget: 3 iterations per prompt.
                              What I observe
                              The Object and Scene streams work well, and objects and environments render about as I'd expect. The trouble is the PostProcess loop. Most prompts never reach an accepted 4D clip within the reflection budget, and the dynamics critic often rejects on motion strength or style even when there is clearly motion in the clip. On a falling-leaves prompt, for instance, the leaves drift visibly across all 240 frames, and the critic still rejects it as too weak ("the trees should sway"). Only a couple of prompts produce a critic-accepted clip; the rest exit unconverged.
                              What I've already ruled out
                              To eliminate my own mistakes first:
                              • I initially ran only Scene + PostProcess, with the Object Stream missing, which broke every object-centric prompt. I fixed that to the full three-phase pipeline from Algorithm 1.
                              • Camera framing, lighting, and exposure look correct on a lit scene: the key object is prominently in frame and moving.
                              • I handle NaN blow-ups from physics parameters (for example, high drag on a very light particle).
                              Questions
                              1. Does the released code include the full PostProcess / 4D-dynamics loop, or is that meant to be rebuilt from the paper? I couldn't get several parts of the dynamics stage running as released, so I want to be sure my version matches yours.
                              2. What is the dynamics critic's accept/reject criterion, and could you share its prompt? This is where most of my runs stall.
                              3. What reflection iteration budget and stopping rule did you use, and how many iterations does a prompt usually take to pass?
                              4. What decoding settings (temperature, max tokens) did you use for the code model and the critic?
                              5. Any guidance for the physics code generation so the motion comes out strong and on-camera enough to pass the critic reliably?
                              6. Roughly what fraction of the Code4D prompts converged into a final 4D clip in your own runs?
                              Happy to share my configs, prompts, and per-iteration critic logs if that would help. Thanks again.
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