The GPT 5.5 Think Deeper Model on Copilot is not responding

Because Think Deeper fails for every licensed user and previously worked, this points to a tenant or service-path problem, not one browser or workstation. Ask a Microsoft 365 administrator to check Health > Service health and the Message center for Copilot advisories. Then use Support > Help and support to run the Copilot service-plan diagnostic for one affected account, confirming the required service is enabled. Compare the same prompt in standard Copilot chat and Think Deeper, using both the web experience and Microsoft 365 Copilot app. Record the UTC failure time, tenant, affected user, selected model, client, region, and any correlation or session identifier. Do not keep changing licenses if the diagnostic reports them correctly. If only Think Deeper fails across clients and accounts, open a Microsoft support case with those results and request service-side investigation. There is no documented local setting that repairs one model for an entire tenant.