Remove unnecessary ACP cost estimation fallback

[simonrosenberg]

Summary

• Removes _estimate_cost_from_tokens() fallback and _last_estimated_cost tracking from acp_agent.py
• Removes 4 associated fallback tests from test_acp_agent.py

The fallback was added in #2326 to estimate cost via litellm.model_cost when the ACP server reported $0. Investigation revealed the $0 was caused by using claude-code-acp@0.16.2 which lacked usage tracking entirely. With claude-agent-acp@0.20.2 (already updated in #2326), the Claude Code SDK correctly computes cost via its internal pricing tables and forwards it through UsageUpdate — making the fallback unnecessary.

Test plan

• All 61 remaining ACP agent tests pass
• CI run-examples workflow confirms ACP example still reports non-zero cost without the fallback

---

Agent Server images for this PR

• GHCR package: https://github.com/OpenHands/agent-sdk/pkgs/container/agent-server

Variants & Base Images

Variant	Architectures	Base Image	Docs / Tags
java	amd64, arm64	eclipse-temurin:17-jdk	Link
python	amd64, arm64	nikolaik/python-nodejs:python3.12-nodejs22	Link
golang	amd64, arm64	golang:1.21-bookworm	Link

Pull (multi-arch manifest)

# Each variant is a multi-arch manifest supporting both amd64 and arm64
docker pull ghcr.io/openhands/agent-server:8cb1c5d-python

Run

docker run -it --rm \
  -p 8000:8000 \
  --name agent-server-8cb1c5d-python \
  ghcr.io/openhands/agent-server:8cb1c5d-python

All tags pushed for this build

ghcr.io/openhands/agent-server:8cb1c5d-golang-amd64
ghcr.io/openhands/agent-server:8cb1c5d-golang_tag_1.21-bookworm-amd64
ghcr.io/openhands/agent-server:8cb1c5d-golang-arm64
ghcr.io/openhands/agent-server:8cb1c5d-golang_tag_1.21-bookworm-arm64
ghcr.io/openhands/agent-server:8cb1c5d-java-amd64
ghcr.io/openhands/agent-server:8cb1c5d-eclipse-temurin_tag_17-jdk-amd64
ghcr.io/openhands/agent-server:8cb1c5d-java-arm64
ghcr.io/openhands/agent-server:8cb1c5d-eclipse-temurin_tag_17-jdk-arm64
ghcr.io/openhands/agent-server:8cb1c5d-python-amd64
ghcr.io/openhands/agent-server:8cb1c5d-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-amd64
ghcr.io/openhands/agent-server:8cb1c5d-python-arm64
ghcr.io/openhands/agent-server:8cb1c5d-nikolaik_s_python-nodejs_tag_python3.12-nodejs22-arm64
ghcr.io/openhands/agent-server:8cb1c5d-golang
ghcr.io/openhands/agent-server:8cb1c5d-java
ghcr.io/openhands/agent-server:8cb1c5d-python

About Multi-Architecture Support

• Each variant tag (e.g., 8cb1c5d-python) is a multi-arch manifest supporting both amd64 and arm64
• Docker automatically pulls the correct architecture for your platform
• Individual architecture tags (e.g., 8cb1c5d-python-amd64) are also available if needed

[github-actions]

API breakage checks (Griffe)

Result: Failed

Log excerpt (first 1000 characters)

============================================================
Checking openhands-sdk (openhands.sdk)
============================================================
Comparing openhands-sdk 1.11.5 against 1.11.4
::notice title=openhands-sdk API::Ignoring Field metadata-only change (non-breaking): load_public_skills
::warning file=openhands-sdk/openhands/sdk/conversation/conversation.py,line=103,title=Conversation.__new__(delete_on_close)::Parameter default was changed: `False` -> `True`
::notice title=openhands-sdk API::Ignoring Field metadata-only change (non-breaking): temperature
::warning file=openhands-sdk/openhands/sdk/llm/llm.py,line=196,title=LLM.top_p::Attribute value was changed: `Field(default=1.0, ge=0, le=1)` -> `Field(default=None, ge=0, le=1, description='Nucleus sampling parameter. Defaults to None (uses provider default). Set to a value between 0 and 1 to control diversity of outputs.')`
::notice title=openhands-sdk API::Ignoring Field metadata-only change (non-breaking): 

Action log

[github-actions]

Agent server REST API breakage checks (OpenAPI)

Result: Failed

Log excerpt (first 1000 characters)

{"asctime": "2026-03-05 19:04:22,177", "levelname": "WARNING", "name": "openhands.agent_server.config", "filename": "config.py", "lineno": 173, "message": "\u26a0\ufe0f OH_SECRET_KEY was not defined. Secrets will not be persisted between restarts."}
::error title=openhands-agent-server REST API::Breaking REST API change detected without MINOR version bump (1.11.4 -> 1.11.5).

Breaking REST API changes detected compared to previous release:
- added '#/components/schemas/GraySwanAnalyzer-Output, #/components/schemas/LLMSecurityAnalyzer-Output' to the '/items/anyOf[subschema #1: ConversationInfo]/security_analyzer/anyOf[subschema #1: LLMSecurityAnalyzer -> #/components/schemas/SecurityAnalyzerBase-Output]/' response property 'oneOf' list for the response status '200'
- the '/items/anyOf[subschema #1: ConversationInfo]/security_analyzer/anyOf[subschema #1: LLMSecurityAnalyzer -> #/components/schemas/SecurityAnalyzerBase-Output]/' response's property type/format changed from 'object'/'' to 

Action log

[all-hands-bot]

Linus-Style Engineering Assessment

🟢 Good taste - This is exactly the kind of cleanup that should happen when you fix the root cause of a problem.

Key Insight: The fallback was a band-aid for using an outdated SDK (claude-code-acp@0.16.2). Once the SDK was updated to claude-agent-acp@0.20.2, the band-aid became unnecessary complexity. Removing ~236 lines of code that solve a problem that no longer exists is good engineering.

Verdict: ✅ Worth merging after verification

Important: This touches cost tracking which could affect benchmarks/evals. Before merging, verify the unchecked test plan item - confirm the CI run-examples workflow shows non-zero cost without the fallback. Once verified, this is a clean simplification with no issues.

[github-actions]

Coverage Report •

File	Stmts	Miss	Cover	Missing
openhands-sdk/openhands/sdk/agent
acp_agent.py	294	55	81%	113–115, 169–172, 174–175, 202, 204, 208, 214, 225–226, 231, 298, 359–360, 397, 407, 412, 423–426, 432–434, 437–439, 441, 443–444, 446, 448, 453, 461–462, 466–467, 471, 478, 481–482, 484, 486–488, 523, 527–528, 652–653
TOTAL	19493	5710	70%

[simonrosenberg]

@neubig you were right to question the necessity of the fallback: bumping the acp version was the real fix

https://github.com/OpenHands/software-agent-sdk/actions/runs/22732193090

[all-hands-bot]

Clean removal of unnecessary fallback logic. The SDK update (claude-agent-acp@0.20.2) fixed the root cause, making this code obsolete. Removing ~236 lines of workaround code is good engineering.