GPT-5.6 Sol hides discovered MCP tools without exposing tool_search

Resolved 💬 4 comments Opened Jul 16, 2026 by ariloudev Closed Jul 17, 2026

What version of Codex CLI is running?

0.144.5

What subscription do you have?

Pro

Which model were you using?

gpt-5.6-sol

What platform is your computer?

Darwin 25.5.0 arm64 arm

What terminal emulator and version are you using (if applicable)?

_No response_

Codex doctor report

{
  "schemaVersion": 1,
  "generatedAt": "1784211109s since unix epoch",
  "overallStatus": "warning",
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        "daemon state dir": "/Users/admin/.codex/app-server-daemon",
        "mode": "ephemeral",
        "pid file": "/Users/admin/.codex/app-server-daemon/app-server.pid (missing)",
        "settings": "/Users/admin/.codex/app-server-daemon/settings.json (missing)",
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        "auth storage mode": "File",
        "stored API key": "false",
        "stored ChatGPT tokens": "true",
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        "config.toml": "/Users/admin/.codex/config.toml",
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        "feature flag overrides": "prevent_idle_sleep=true",
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        "git build options": "git version 2.50.1 (Apple Git-155); cpu: arm64; no commit associated with this build; sizeof-long: 8; sizeof-size_t: 8; shell-path: /bin/sh; feature: fsmonitor--daemon; libcurl: 8.7.1; zlib: 1.2.12; SHA-1: SHA1_DC; SHA-256: SHA256_BLK",
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      "remediation": "Set the missing MCP env vars or disable the affected server.",
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      "summary": "Responses WebSocket handshake succeeded",
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        "auth mode": "chatgpt",
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        "endpoint": "wss://chatgpt.com/backend-api/<redacted>",
        "handshake result": "HTTP 101 Switching Protocols",
        "model provider": "openai",
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        "proxy env vars": "none",
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    "runtime.search": {
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        "search command readiness": "ripgrep 15.1.0",
        "search provider": "system"
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    "sandbox.helpers": {
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      "status": "ok",
      "summary": "sandbox configuration is readable",
      "details": {
        "approval policy": "OnRequest",
        "codex-linux-sandbox helper": "none",
        "execve wrapper helper": "/Users/admin/.codex/tmp/arg0/codex-arg0pFSY38/codex-execve-wrapper",
        "filesystem sandbox": "restricted",
        "network sandbox": "restricted"
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      "remediation": null,
      "durationMs": 0
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    "state.paths": {
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      "category": "state",
      "status": "ok",
      "summary": "state paths and databases are inspectable",
      "details": {
        "CODEX_HOME": "/Users/admin/.codex (dir)",
        "active rollout files": "735 files, 796735971 total bytes, 1083994 average bytes",
        "archived rollout files": "0 files, 0 total bytes, 0 average bytes",
        "goals DB": "/Users/admin/.codex/goals_1.sqlite (file)",
        "goals DB integrity": "ok",
        "log DB": "/Users/admin/.codex/logs_2.sqlite (file)",
        "log DB integrity": "ok",
        "log dir": "/Users/admin/.codex/log (dir)",
        "memories DB": "/Users/admin/.codex/memories_1.sqlite (file)",
        "memories DB integrity": "ok",
        "sqlite home": "/Users/admin/.codex (dir)",
        "state DB": "/Users/admin/.codex/state_5.sqlite (file)",
        "state DB integrity": "ok"
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      "summary": "rollout files and state DB thread inventory agree",
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        "rollout DB model providers": "openai=735",
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    "system.environment": {
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      "status": "ok",
      "summary": "OS language en-US",
      "details": {
        "EDITOR": "not set",
        "LANG": "C.UTF-8",
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        "last checked at": "2026-07-16T13:09:51.525097Z",
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  }
}

What issue are you seeing?

Summary

Codex CLI 0.144.5 successfully discovers all eight tools from a local
synthetic MCP server, but a fresh gpt-5.6-sol session exposes neither the
MCP tools nor tool_search.

The same server, configuration, and prompt work with gpt-5.4.

### Environment

Codex CLI: 0.144.5
macOS 26.5.2, Apple Silicon
Native OpenAI provider with ChatGPT authentication
MCP: unauthenticated Streamable HTTP
Failing model: gpt-5.6-sol
Working model: gpt-5.4
Reproduction server: https://github.com/ariloudev/mcp-test

What steps can reproduce the bug?

### Reproduction

Start the synthetic server:

``bash git clone https://github.com/ariloudev/mcp-test cd mcp-test uv sync .venv/bin/python server.py``

``bash codex mcp add kraka --url http://127.0.0.1:8000/mcp``

The server exposes eight deterministic tools, including echo. Direct
tools/list returns all eight successfully.

Run:

``bash codex -m gpt-5.6-sol \ --dangerously-bypass-approvals-and-sandbox \ exec --skip-git-repo-check \ 'Use the registered kraka MCP echo tool directly with message "hello from Codex". Do not use shell commands, curl, Python, filesystem inspection, MCP resources, or protocol-level HTTP. Report the returned value.'``

Actual result:

``text I can’t call the registeredkrakaecho tool because it isn’t exposed in this session’s available tools.``

Codex logs nevertheless confirm discovery:

``text listed MCP server tools while building tool list server_name=kraka tool_count=8``

No tool_search_call or MCP function call occurs.

Repeat with gpt-5.4:

``bash codex -m gpt-5.4 \ --dangerously-bypass-approvals-and-sandbox \ exec --skip-git-repo-check \ 'Use the registered kraka MCP echo tool directly with message "hello from Codex". Do not use shell commands, curl, Python, filesystem inspection, MCP resources, or protocol-level HTTP. Report the returned value.'``

This succeeds:

``text mcp: kraka/echo started mcp: kraka/echo (completed) Returned value:hello from Codex``

The GPT-5.4 rollout contains:

``text tool_search_call → tool_search_output containing mcp__kraka → mcp__kraka/echo → "hello from Codex"``

### Diagnostics

``text tool_search removed false tool_search_always_defer_mcp_tools removed true``

Model metadata:

``text gpt-5.6-sol: supports_search_tool=true, use_responses_lite=true gpt-5.4: supports_search_tool=true, use_responses_lite=false``

What is the expected behavior?

### Expected behavior

If Codex defers MCP tools, it must expose tool_search. If tool_search is
unavailable, the MCP tools must remain directly callable.

Additional information

### Suspected cause

This appears specific to the GPT-5.6 Sol Responses Lite path: Codex defers
the discovered MCP tools but omits the client-side tool_search required to
load them.

Potentially related changes:

[#29486 — Use tool search for MCP tools by default](https://github.com/

openai/codex/pull/29486)

[#27946 — Use input items for Responses Lite tools](https://github.com/

openai/codex/pull/27946)

Related report: #19425

View original on GitHub ↗

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