Xiaomi says MiMo-V2.6 repeated tool calls were caused by RL design, fixes issue for about $90,000

Xiaomi’s MiMo team said it has identified and fixed a repeated tool-calling issue that appeared after the launch of MiMo-V2.6. In some cases, the model would call the same or highly similar tools over and over, consuming context without making progress on the task. In OpenCode, the share of responses with repeated tool calls at one point reached 1.02% for Flash and 0.54% for Pro. According to the team, the problem came from reinforcement learning reward design. Training heavily rewarded whether the final task was completed correctly, but did not penalize inefficient behavior enough during the process. Under the original rule, penalties applied only when tool calls in a single round exceeded 32, which left repeated calls below that threshold unpunished. Xiaomi said this behavior became more pronounced as RL scaled up. Instead of a full retraining plan that would have required lowering the penalty threshold to 8, rerunning about 20 MixRL steps, and spending an estimated $2.31 million, Xiaomi trained a dedicated RL teacher to correct repeated calls. The fix used 12 steps and about 7,000 samples, then merged the capability back into Pro and Flash through MOPD. Xiaomi said the full repair cost about $90,000, roughly 4% of the full retraining option, while other major benchmarks were largely unchanged.