# Classic configuration files

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Fluent Bit classic mode configuration will be deprecated at the end of 2026.
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Classic mode is a custom configuration model for Fluent Bit. It's more limited than the [YAML configuration mode](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/yaml), and doesn't have the more extensive feature support the YAML configuration has. Classic mode basic design only supports grouping sections with key-value pairs and lacks the ability to handle sub-sections or complex data structures like lists.

Learn more about classic mode:

* [Format and schema](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/format-schema)
* [Variables](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/variables)
* [Configuration file](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/configuration-file)
* [Commands](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/commands)
* [Upstream servers](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/upstream-servers)
* [Record accessor syntax](https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/record-accessor)