# Opus 4.6 fast mode not accessible via ACP **URL:** \ **Category:** Bug Reports\ **Tags:** acp, cli, anthropic\ **Created:** [April 24, 2026, 2:21pm UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943 "2026-04-24T14:21:02Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![rohitpaulk](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/rohitpaulk/32/469_2.png) [@rohitpaulk](https://forum.cursor.com/u/rohitpaulk)\ **Post date:** [April 24, 2026, 2:21pm UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/1 "2026-04-24T14:21:02Z")
### Where does the bug appear (feature/product)? Cursor CLI ### Describe the Bug When running the CLI in ACP mode, Opus 4.6 fast mode isn’t listed. ### Steps to Reproduce - Run `agent models` , you’ll see that Opus 4.6 fast mode is present - Run `agent acp` and you’ll see that Opus 4.6 fast mode is NOT present Since the ACP thing is a bit tricky to test, I created a repro script here: [GitHub - rohitpaulk/cursor-acp-models-repro · GitHub](https://github.com/rohitpaulk/cursor-acp-models-repro). ### Expected Behavior Expected that Opus 4.6 fast mode is present in ACP mode too. ### Screenshots / Screen Recordings ![Screenshot 2026-04-24 at 19.49.25.png](https://us1.discourse-cdn.com/cursor1/original/3X/e/0/e0e6b9ba3da26876531d463c7c383ca24d296904.png) ### Operating System MacOS ### Version Information About Cursor CLI CLI Version 2026.04.17-787b533 Model Opus 4.6 1M Thinking Fast Subscription Tier Team OS darwin (arm64) Terminal zed Shell zsh ### Does this stop you from using Cursor Sometimes - I can sometimes use Cursor ---
**Author:** ![Jurij\_Gera](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/jurij_gera/32/103209_2.png) [@Jurij\_Gera](https://forum.cursor.com/u/Jurij_Gera)\ **Post date:** [April 27, 2026, 5:53am UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/5 "2026-04-27T05:53:13Z")
I confirm. Right now it is not possible to select newer Clause/Opus or GPT models in ACP. Some important model effort configurations are missing. Max mode / 1M token configs are missing entirely. I did basic test asking each model what model it is. Response "_Check your settings to continue"_ insicates that something is wrong with the model config. Perhaps on the backend side. May be there is some hidden config in user/team/admin settings which was forgotten to turn on. Right now only 15 out of 27 models, mostly old ones, are working. Another fun fact: If I start cursor-agent CLI and specify model: cursor-agent --model gpt-5.5-extra-high “What model are you?” And then after this run ACP without specifying model, the ACP will show its previously selected model which is actually stale, in the reality the prompts will be answered by real model previously selected by cursor-agent --model, so in this case GPT 5.5 So all models and all settings, even the 1M token ones, work just fine in ACP mode, its just the ACP model selection which is broken. My test results: `[22:44:28.609] ==== scan results ====` `[22:44:28.609] claude-haiku-4-5[thinking=true] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] claude-opus-4-5[thinking=true] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] claude-opus-4-6[thinking=true,context=200k,effort=high,fast=false] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] claude-opus-4-7[thinking=true,context=200k,effort=xhigh] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] claude-sonnet-4-5[thinking=true,context=200k] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] claude-sonnet-4-6[thinking=true,context=200k,effort=medium] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] claude-sonnet-4[thinking=false,context=200k] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] composer-1.5``→ stopReason=‘end_turn’; response=‘I am` **`Composer`** `, a language model from Cursor, trained by Cursor. I don’t have a more specific public model name or build ID in this environment beyond that.’` `[22:44:28.610] composer-2[fast=true] → stopReason=‘end_turn’; response=‘I’m ` **`Composer`** `, Cursor’s coding assistant. The conversation context I get does ` **`not`** ` include a concrete backend model slug or version ID (e.g. a specific GPT/Claude build name), so I can’t give an exact model ID beyond that.’` `[22:44:28.610] default``→ stopReason=‘end_turn’; response=‘I don’t get a concrete model slug or ID in my runtime context, so I can’t give you an exact string I can verify (for example gpt-4.1 vs another name). / What I`_`do`_`know from this session: I’m` **`Auto`** `, Cursor’s ` **`agent router`** `—the layer that picks and coordinates models/tools for you. The underlying chat model is chosen by your Cursor settings and isn’t exposed to me as a labeled field I can quote. / To see the exact model for this chat: use Cursor’s model picker / chat settings for this conversation, or check your account/workspace AI preferences where the active model is shown.’` `[22:44:28.610] gemini-2.5-flash`` → stopReason=‘end_turn’; response=‘I am powered by Gemini 2.5 Flash.’` `[22:44:28.610] gemini-3-flash`` → stopReason=‘end_turn’; response=‘I am using the Gemini 1.5 Flash model.’` `[22:44:28.610] gemini-3.1-pro``→ stopReason=‘end_turn’; response=‘I am using the` **`Gemini 3.1 Pro`** ` model.’` `[22:44:28.610] gpt-5-mini`` → stopReason=‘end_turn’; response=‘gpt-5-mini’` `[22:44:28.610] gpt-5.1-codex-max[reasoning=medium,fast=false] → stopReason=‘end_turn’; response=‘I’m running on the gpt-5.1-codex-max model.’` `[22:44:28.610] gpt-5.1-codex-mini[reasoning=medium] → stopReason=‘end_turn’; response=‘I’m using GPT-5.1 Codex Mini.’` `[22:44:28.610] gpt-5.1[reasoning=medium] → stopReason=‘end_turn’; response=‘I’m running as ` **`GPT-5.1`** `, accessed via this coding agent interface.’` `[22:44:28.610] gpt-5.2-codex[reasoning=medium,fast=false] → stopReason=‘end_turn’; response=‘I don’t have access to the exact model name or ID in this environment.’` `[22:44:28.610] gpt-5.2[reasoning=medium,fast=false] → stopReason=‘end_turn’; response=‘` **`GPT-5.2`** `’` `[22:44:28.610] gpt-5.3-codex-spark[reasoning=medium] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] gpt-5.3-codex[reasoning=medium,fast=false] → stopReason=‘end_turn’; response=‘Codex 5.3’` `[22:44:28.610] gpt-5.4-mini[reasoning=medium] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] gpt-5.4-nano[reasoning=medium] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] gpt-5.4[context=272k,reasoning=medium,fast=false] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] gpt-5.5[context=272k,reasoning=medium,fast=false] → stopReason=‘end_turn’; response=‘Check your settings to continue’` `[22:44:28.610] grok-4-20[thinking=true] → stopReason=‘end_turn’; response=‘` **`grok-4-20`** `/ (That’s the exact model ID from the Cursor CLI config: modelId: "grok-4-20", displayed as`**`Grok 4.20 (Thinking)`**` with the thinking parameter enabled.)’` `[22:44:28.610] kimi-k2.5``→ stopReason=‘end_turn’; response=‘I am using` **`Kimi K2.5`** `.’` `[22:44:28.610] ==== /scan results ====` ---
**Author:** ![kevinn](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/kevinn/32/101206_2.png) [@kevinn](https://forum.cursor.com/u/kevinn)\ **Post date:** [April 28, 2026, 3:32am UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/8 "2026-04-28T03:32:05Z")
Hi Paul, Thanks for the post! This is a known ACP model-selection limitation we’ve seen with reasoning / variant selection. Right now, ACP model selection is not exposing the full set of model parameters and variants consistently, including fast mode / Max Mode / 1M-context variants. That’s why `agent models` can show Opus 4.6 1M Thinking Fast while `agent acp` does not present it as an available option. We’re tracking this internally. The desired behavior is that ACP clients can either surface these variants directly or expose the underlying model parameters clearly, rather than collapsing them down to a smaller/default set. For now, if you need precise control over Opus 4.6 fast / 1M settings, the Cursor editor or regular CLI model selection is the more reliable path. Check out this thread for more info: [IntelliJ Cursor ACP Reasoning Levels - #4 by kevinn](https://forum.cursor.com/t/intellij-cursor-acp-reasoning-levels/158975/4) ---
**Author:** ![Jurij\_Gera](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/jurij_gera/32/103209_2.png) [@Jurij\_Gera](https://forum.cursor.com/u/Jurij_Gera)\ **Post date:** [April 29, 2026, 10:00pm UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/9 "2026-04-29T22:00:39Z")
Hi Kevin, thanks. Limitation of the CLI is that it does not expose an API which can be used to do safety reviews and approvals of the tool invocations. Unchecked auto-approvals are risky and whitelists are limited, often both are locked entirely. ACP has been the best option as it allows verification of the tool invocations, i.e. one can use another LLM for verification to contain the risks. Overall ACP is a more functional interface to controlling agents, but the model selection issue limits it use. ---
**Author:** ![Jurij\_Gera](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/jurij_gera/32/103209_2.png) [@Jurij\_Gera](https://forum.cursor.com/u/Jurij_Gera)\ **Post date:** [May 4, 2026, 8:46pm UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/10 "2026-05-04T20:46:55Z")
In the new cursor-agent version 2026.05.01 model selection works for all 28 preset models. Thanks for resolving the issue. The only remaining limitation: none of the model presets provide 1M context ---
**Author:** ![kevinn](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/kevinn/32/101206_2.png) [@kevinn](https://forum.cursor.com/u/kevinn)\ **Post date:** [May 4, 2026, 9:54pm UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/11 "2026-05-04T21:54:18Z")
Hi @Jurij_Gera, yes that appears to still be a relevant limitation. If you’re able to use the CLI, that would be a good workaround. You use the tab button to edit the model config as shown below, and you can use 1M context there. But ACP via things like IntelliJ don’t yet support editing the context. ![Screenshot 2026-05-04 at 2.52.27 PM](https://us1.discourse-cdn.com/cursor1/original/3X/4/8/484c5918825f4d0297b7babd211185b488704469.png) ---
**Author:** ![system](https://sea3.discourse-cdn.com/cursor1/user_avatar/forum.cursor.com/system/32/99069_2.png) [@system](https://forum.cursor.com/u/system)\ **Post date:** [June 25, 2026, 9:48pm UTC](https://forum.cursor.com/t/opus-4-6-fast-mode-not-accessible-via-acp/158943/13 "2026-06-25T21:48:54Z")
Closed on June 25, 2026, 9:48pm UTC This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.