The trial is a multicentre, prospective, open-label, blinded endpoint (PROBE), phase 3, randomized controlled design. Patients with acute ischemic stroke due to basilar artery occlusion presenting within 24 hours will be randomized 1:1 to intravenous tenecteplase (0.25mg/kg, maximum 25mg) ± thrombectomy or 'best practice'which may be alteplase (0.9mg/kg) within 4.5 hours from stroke onset or standard care (no lysis) ± thrombectomy at treating clinician's discretion.

The study will be a multicentre, prospective, open-label, blinded endpoint (PROBE), randomized controlled trial (2 arm with 1:1 randomization) in patients with acute ischemic stroke due to basilar artery occlusion presenting to hospital within 24 hours of symptom onset.

Patients will be required to have complete or near-complete occlusion of the basilar artery on baseline computed tomography angiography (CTA)/magnetic resonance angiography (MRA), defined as 'potentially retrievable' thrombus in the basilar artery. Thrombectomy is permitted within 24 hours as part of standard care but is not mandatory.

Patients will be randomized to treatment with either standard of care (no intravenous thrombolytic treatment or intravenous alteplase 0.9mg/kg within 4.5 hours from stroke onset) or intravenous tenecteplase (0.25mg/kg, maximum 25mg). Time of onset of symptoms is defined as described by the patient or witness; if unknown, it is considered to be the last time the patient was seen well. In patients presenting with mild (e.g. vertigo, dizziness, headache, diplopia, dysarthria) stuttering symptoms followed by sudden onset of clinical deterioration with decrease in conscious state or moderate to severe motor deficits, the time of deterioration in clinical state is taken as the estimated time of basilar artery occlusion.

Inclusion Criteria:

1. Age ≥18.
2. Patients presenting with posterior circulation ischemic stroke symptoms due to near-complete or complete basilar artery occlusion within 24 hours from symptom onset (or clinical deterioration/coma) or the time the patient was last known to be well.
3. Presence of a basilar artery occlusion, proven by CT Angiography or MR Angiography. Basilar artery occlusion will be defined as 'potentially retrievable' occlusion at the basilar artery. This can be a near or complete occlusion.
4. Premorbid mRS ≤3 (independent function or requiring only minor domestic assistance and able to manage alone for at least 1 week).
5. Local legal requirements for consent have been satisfied.

Exclusion Criteria:

1. Intracerebral haemorrhage (ICH) or other diagnosis (e.g. tumour) identified by baseline imaging.
2. Posterior circulation Acute Stroke Prognosis Early CT Score (PC-ASPECTS) <6 on non-contrast CT (NCCT) or CTA-source images or MRI diffusion weighted imaging (DWI).
3. Significant cerebellar mass effect or acute hydrocephalus.
4. Established frank hypodensity on non-contrast CT indicating subacute infarction.
5. Bilateral extensive brainstem ischemia.
6. Pre-stroke mRS of ≥4 (indicating moderate to severe previous disability).
7. Other standard contraindications to intravenous thrombolysis.
8. Contraindication to imaging with contrast agents.
9. Clinically evident pregnant women.
10. Vessel imaging showing both anterior and posterior circulation large vessel occlusion.
11. Current participation in another research drug treatment protocol.
12. Known terminal illness such that the patients would not be expected to survive a year.
13. Planned withdrawal of care or comfort care measures.
14. Any condition that, in the judgment of the investigator could impose hazards to the patient if study therapy is initiated or affect the participation of the patient in the study.