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mid_model_research/forgecode/feedback/frontier/gpt-5.4.md
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sleepy 51123212c4 Initial commit: coding harness feedback analysis
Harnesses under analysis:
- opencode (Go-based coding agent)
- pi (minimal terminal coding harness by Mario Zechner)
- hermes (Nous Research agent)
- forgecode (AI pair programmer with sub-agents)

Each harness folder contains:
- repo/: Source code from respective repositories
- feedback/localllm/: Community feedback for local/smaller models
- feedback/frontier/: Community feedback for frontier models

Research focus: Tool handling, skills systems, prompt engineering,
context management, and best practices for smaller/local models.
2026-04-09 15:13:45 +02:00

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# GPT 5.4 with ForgeCode - Feedback Report
**Model:** GPT 5.4
**Provider:** OpenAI
**Harness:** ForgeCode
**Source References:** DEV Community (Liran Baba), ForgeCode Blog
**Date Compiled:** April 9, 2026
---
## Benchmark Performance
### TermBench 2.0 (Self-Reported via ForgeCode)
- **Score:** 81.8% (tied for #1 with Opus 4.6)
- **Note:** Achieved through extensive harness optimizations, not raw model capability
---
## Real-World Performance Feedback
### Stability Issues
- **Assessment:** "Borderline unusable" for some tasks
- **Specific Issue:** 15-minute research task on small repo
- Tool calls repeatedly failing
- Agent stuck in retry loops
- Required manual kill
> "I asked it to research the architecture of a small repo. Fifteen minutes. Kept going unstable, tool calls failing, the agent retrying and spinning. I killed it."
### Tool Calling Reliability
- **Problem:** Persistent tool-call errors with GPT 5.4
- **ForgeCode Fixes Applied:**
1. Reordered JSON schema fields (`required` before `properties`)
2. Flattened nested schemas
3. Added explicit truncation reminders for partial file reads
- **Result:** These optimizations were benchmark-specific (described as "benchmaxxed")
---
## Harness Optimizations for GPT 5.4
From ForgeCode's "Benchmarks Don't Matter" blog series:
1. **Non-Interactive Mode:** System prompt rewritten to prohibit conversational branching
2. **Tool Naming:** Renaming edit tool arguments to `old_string` and `new_string` (names appearing frequently in training data) measurably dropped tool-call error rates
3. **Progressive Thinking Policy:**
- Messages 1-10: Very high thinking (plan formation)
- Messages 11+: Low thinking default (execution phase)
- Verification skill calls: Switch back to high thinking
---
## What Didn't Work Well
1. **Research tasks:** Tool calling failures causing infinite loops
2. **Long-running tasks:** 15+ minute tasks became unstable
3. **Consistency:** Unpredictable failures requiring manual intervention
---
## Comparison with Opus 4.6
| Aspect | GPT 5.4 | Opus 4.6 |
|--------|---------|----------|
| TermBench 2.0 | 81.8% | 81.8% |
| Real-world stability | Poor | Excellent |
| Tool calling reliability | Problematic | Reliable |
| Research tasks | Unusable | Good |
**Key Takeaway:** Benchmark scores don't reflect real-world usability. Same harness, dramatically different experiences.
---
## Source References
1. **DEV Community:** https://dev.to/liran_baba/forgecode-vs-claude-code-which-ai-coding-agent-actually-wins-36c
2. **ForgeCode Blog:** https://forgecode.dev/blog/benchmarks-dont-matter/