[BUG] Prompt suggestions send a second full-context model call per turn, ~doubling token usage

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

With prompt suggestions enabled (the default), Claude Code sends a second, separate model request on every turn — a "suggestion mode" call that carries the entire conversation and the full tool list. Because it's full-context, it costs almost as much as the actual reply, roughly doubling per-turn token / quota consumption. Nothing in the UI indicates a second billed call is happening.

I confirmed it by routing the client through a local proxy and reading the usage field of every POST /v1/messages response. Per user turn I see two claude-sonnet-5 requests:

1. the reply (input=2, tiny)
2. a second request whose system prompt starts with [SUGGESTION MODE: Suggest what the user might naturally type next into Claude Code.], carrying n_msgs=20, all 42 tool definitions, and ~60k tokens of cached context.

Setting CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=false removes the second request entirely, which confirms the suggestion feature is the cause.

What Should Happen?

Generating a next-prompt suggestion should not cost as much as answering the user. Either:

• make suggestions opt-in, or
• generate them with a cheaper model (e.g. Haiku) and a trimmed context instead of the full conversation + all tool definitions, or
• at minimum, surface that suggestions issue a separate billed model call.

Error Messages/Logs

Captured token usage for a single ok turn (warm cache), via mitmproxy reading the usage field. No secrets included — token counts only.

Before (default, suggestions on) — two Sonnet calls per turn:

| call | model | input | cache_read | cache_write | output |
|------|-------|-------|-----------|-------------|--------|
| reply | claude-sonnet-5 | 2 | 60,381 | 68 | 4 |
| suggestion | claude-sonnet-5 | 504 | 60,449 | 4 | 9 |

Suggestion request system prompt begins:

[SUGGESTION MODE: Suggest what the user might naturally type next into Claude Code.]

After (CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION=false) — one Sonnet call per turn:

| call | model | input | cache_read | cache_write | output |
|------|-------|-------|-----------|-------------|--------|
| reply | claude-sonnet-5 | 2 | 59,956 | 0 | 4 |

Steps to Reproduce

1. Start a local intercepting proxy: mitmdump -s capture.py, where the addon parses the usage field of each POST /v1/messages response (input_tokens/cache_* from the message_start SSE event, output_tokens from message_delta).
2. Point Claude Code at it: set HTTPS_PROXY=http://127.0.0.1:8080 and NODE_EXTRA_CA_CERTS to the mitmproxy CA cert (the Node client ignores the OS cert store). Restart the app.
3. Send a prompt that triggers no tools and a fixed reply: Reply with exactly the word ok and nothing else. Do not use any tools.
4. Observe two claude-sonnet-5 requests per turn — the reply and a [SUGGESTION MODE...] request carrying full context.
5. Add "CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION": "false" to the env block in settings.json, restart, repeat step 3 — now only one request per turn.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.241

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Other

Additional Information

• Workaround for anyone hitting this: add "env": { "CLAUDE_CODE_ENABLE_PROMPT_SUGGESTION": "false" } to settings.json.
• Related: #74826 (acknowledges suggestions carry a token cost, but frames it as an opt-in tradeoff — this report shows it is on by default and full-context), #52979 (baseline overhead for trivial prompts).