diff --git a/stacks/gen-seat/compose.yaml b/stacks/gen-seat/compose.yaml
index 2cfff28..ef23a45 100644
--- a/stacks/gen-seat/compose.yaml
+++ b/stacks/gen-seat/compose.yaml
@@ -62,21 +62,13 @@ services:
       - '{"image": 4}'
       - --reasoning-parser
       - ${GEN_REASONING_PARSER:-qwen3}
-      # Seat-level DEFAULT reasoning effort, per-request overridable via
-      # chat_template_kwargs. The AEON-ULTIMATE chat template defaults to
-      # `xhigh` (template line 47), and at xhigh this model can spend its ENTIRE
-      # token budget inside <think> -- the block runs past 18k chars, sometimes
-      # degenerating into repeating one line, and no answer is ever emitted.
-      # That is a silent-empty-response hazard for the automated consumers on
-      # this seat (`summarizer`, `classifier`), so the default is pinned down a
-      # notch rather than left at the model's own.
-      # Template accepts ONLY xhigh | medium | low and RAISES on anything else,
-      # so a typo in a caller's chat_template_kwargs is a 400, not a silent
-      # fallback. Empty value = omit the flag entirely (pre-AEON models such as
-      # the Qwen3.6 line do not read this kwarg at all, and setting it there
-      # would be a false lever).
-      - --default-chat-template-kwargs
-      - '{"reasoning_effort": "${GEN_REASONING_EFFORT:-medium}"}'
+      # NOTE: a --default-chat-template-kwargs '{"reasoning_effort": "medium"}'
+      # line lived here during the 2026-08-16 AEON-ULTIMATE trial and was
+      # REMOVED on rollback, so that restoring the previous model restores the
+      # previous behaviour exactly and the model stays the only changed
+      # variable. Re-add it only alongside a template that actually reads the
+      # kwarg (AEON's does, at chat_template.jinja:47; the Qwen3.6 line ignores
+      # it entirely, where setting it would be a false lever).
       - --enable-auto-tool-choice
       - --tool-call-parser
       - qwen3_coder