Upgrade Odoo 12 to Odoo 20

1. 13 October 2019

   Odoo 13: Invoices Become Journal Entries

   • account.invoice is merged into account.move, so custom invoice code and reports need rework.
   • The @api.multi and @api.one decorators are removed, and every method now works on multiple records.
   • sudo(user) becomes with_user(user), and track_visibility becomes tracking=True.
2. 14 October 2020

   Odoo 14: Actions and Multi-Company Code Change

   • The act_window and report shortcut tags are removed, so actions and reports must be full XML records.
   • The force_company context is replaced by with_company() for multi-company code.
   • Fields that extend a selection need an ondelete mapping, and transient models need access rights.
3. 15 October 2021

   Odoo 15: Assets Move Into the Module Manifest

   • JavaScript and SCSS assets are declared in the manifest instead of XML templates.
   • QWeb t-raw is replaced by t-out across views, reports, and website templates.
   • Mail templates move from Jinja to QWeb and a new inline placeholder syntax, so custom email templates need rewriting.
4. 16 October 2022

   Odoo 16: Analytic Accounting Is Rebuilt

   • Analytic accounting moves to analytic plans and distributions, which changes how cost tracking data is stored.
   • Reports, QWeb templates, and website pages move from Bootstrap 4 to Bootstrap 5.
   • fields_view_get is replaced by get_view, and the old flush and cache methods are replaced by granular ones.
5. 17 November 2023

   Odoo 17: attrs and states Leave the Views

   • Every conditional field rule written with attrs or states becomes a Python expression.
   • name_get is replaced by _compute_display_name, which affects how custom records show their names.
   • Install and uninstall hooks now receive env, and settings screens use new app, block, and setting tags.
6. 18 October 2024

   Odoo 18: Tree Views Become List Views

   • Tree views are renamed list views, including the tree_view_ref context key.
   • user_has_groups, check_access_rights, and check_access_rule give way to has_group and check_access.
   • Chatter and kanban markup change, with a single chatter tag and card templates for kanban views.
7. 19 September 2025

   Odoo 19: New Constraints and Security Groups

   • SQL constraints move from _sql_constraints to models.Constraint and models.Index attributes.
   • groups_id becomes group_ids, and group categories become privileges.
   • read_group is replaced by _read_group or formatted_read_group, and JSON routes use type="jsonrpc".
8. 20 September 2026

   Odoo 20: Record Rules Give Way to Access Domains

   • Record rules are removed, and access is set with a domain on each access right, so custom security must be rebuilt.
   • The Field Service app is discontinued and its features move into Planning.
   • Stored mail tracking values are removed and tracking messages are built on the fly, so custom reports on tracking data need rework.

The OCA migration guides for Odoo 13 to 19, the Odoo 20 release notes, and Odoo's supported versions page.