mainLoopModel
A Claude Code settings key, read out of the shipped bundle. It was in the build from v2.1.315 and was gone by v2.1.317.
Workflow-spawned agents resolve a model themselves before falling back to the main one.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.251.
In the changelogs
6Releases whose published page names mainLoopModel.
-
v2.1.281
Precomputed compact arm fraction computed from a new 'facts' input
A precomputed-compaction value is now worked out from a new "facts" input instead of straight from the main model setting
found in this entry's text
-
v2.1.273
Tool-execution hook context object substantially reworked
The context object passed to tool-execution hooks was substantially reworked with many new fields
found in this entry's text
-
v2.1.251
Workflow-spawned agents resolve their own model before inheriting
Workflow-spawned agents resolve a model themselves before falling back to the main one.
found in this entry's text
-
v2.1.165
Extended Thinking Support in Conversation Summarizer
found in this entry's text
-
v2.1.126
Read-tool no longer injects a model-specific malware-analysis system reminder
found in this entry's text
-
v0.2.115
Technical Changes
found in this entry's text
First cited
7The earliest release whose published evidence quoted mainLoopModel was v2.1.165, 5 Jun 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
1 further span in the ledger name it. The list above is the earliest first and stops at 6.
Presence across releases
2Build by build
7One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the settings key does. All settings keys.